If you have been practicing black hat SEO (namely using link farms and getting links from dubious sites or content spamming - using the same keywords over and over while attaching internal links to them) then you may not get your ranking back.

May be your site has been affected with updates,if that's the case try to resolve the issues and submit your website.The another reason can be your competitors are working better than you to rank higher.Check for competitors and analyse their work and prepare your strategy.

I would like to tell you about 5 reasons why rankings can drop:- your website lost links;- you have changed yourself-promotion; - Google changed their algorithm; - your web content is stale; - your competitors have gotten better.

Reasons for Rank drop Backlinks aren't as popularYour site contains malware or virusesText that is hiddenYour site has poor quality contentyou are linking to bad sitesyour server is consistenly downyou have dublicate content on your site